There is a wide variety of methods for forming a coating or deposited material. Methods include chemical vapor deposition, physical vapor deposition, laser assisted pyrolysis deposition, electron-beam physical vapor deposition and thermal spray. The coating or material produced by these methods can vary significantly in microstructure from method to method. The microstructure of the coating or material, as well as its composition, has a significant impact the physical and mechanical properties, as well as the end use. Thus it is clear that there is a complex interaction between the microstructure, composition, end use and the method of making the coating or material.
Microstructure, as used herein, refers to the structure of the material or coating on a microscopic level. Components of microstructure include the phases present, grain size, precipitate and/or dispersoid size, density/porosity, cracking, and the presence and size of lamellar splats (in thermal spray methods). Splats are the result of molten or partially molten particles impinging upon a substrate at a high temperature, high speed or combination of high temperature and high speed. The size of the splat boundary is related to the size of the splat and large splat boundaries may result in lateral cracking, potentially causing material failure. These components of microstructure may affect gross physical properties of the coating such as thermal conductivity, bond strength, elastic modulus and so forth. As can be readily appreciated some of these gross physical characteristics are desirable in some uses and not in others. None of the currently available methods of deposition is capable of manipulating all the above-described microstructural features.
Of the above-described methods, thermal spray is the most flexible with regard to feedstocks. Thermal spray may employ a solid, powdered feedstock, a dispersion of a solid, powdered feedstock in a liquid carrier, or a liquid precursor. Thermal spray is highly flexible with regard to the composition of the feedstock owing to the variety of available flame types, velocities and flame temperatures and resulting in a wide compositional variety in the produced materials. Additionally, thermal spray generally is highly efficient making it a cost effective method.
What is needed in the art is a cost effective method of material deposition that can produce materials and coatings with a variety of compositions and microstructural features.